df <- data.frame(a=runif(1:100), b=runif(1:100), c=runif(1:100), d=runif(1:100), e=runif(1:100), f=runif(1:100))

summary(lm(a ~ b * (c + d + e + f), data = df))

summary(lm(a ~ b*c + d + e + f, data = df))
summary(lm(a ~ c + b*d + e + f, data = df))
summary(lm(a ~ c + d + b*e + f, data = df))
summary(lm(a ~ c + d + e + b*f, data = df))